Lindsey, I've been wondering about what really happens after transplant in regards to breath training. I am not so sure it's the lungs we have to work so hard to "open up". Pretty sure they're ready to go, especially after viewing videos of lungs in the ex-vivo perfusion machine and seeing them definitely inflate and deflate a great deal!
Rather, I suspect it is our diaphragms that need extensive re-training. After all, we've just spent years unable to draw deep or quick breaths - like any muscle, our diaphragms will de-train. But, given a renewed lung capacity to work with, we can certainly re-train the diaphragm to pull bigger and bigger lungfuls of air, faster and faster until we hit a peak near or exceeding normal capacity.